The present invention relates to a high frequency power amplifier module for obtaining a predetermined amplification factor by cascade connecting a plurality of heterojunction bipolar transistors, and a wireless communication apparatus in which the high frequency power amplifier module is assembled. More particularly, the invention relates to a technique effective for improving destruction resistance of a heterojunction bipolar transistor to fluctuations in load impedance.
At an input stage of a transmitter of a wireless communication apparatus (mobile communication apparatus) such as an automobile telephone or portable telephone, an amplifier (high frequency power amplifier module, or RF power module) in which MOSFETs (Metal Oxide Semiconductor Field-Effect-Transistors), GaAs-MES (Metal-Semiconductor) FETs, HEMTs (High Electron Mobility Transistors), or HBTs (Heterojunction Bipolar Transistors) are formed at multiple stages is assembled.
The heterojunction bipolar transistor (HBT) is described in, for example, xe2x80x9cA robust 3W high efficiency 8-14 Ghz GaAs/AlGaAs heterojunction bipolar transistor power amplifierxe2x80x9d, IEEE-MTTS, p581-584. This literature discloses a multi-finger HBT structure using cascade connection to improve destruction resistance of the HBT. Specifically, by using cascaded HBTs for each finger, a hot spot caused by concentration of currents can be suppressed, a breakdown voltage is increased, and destruction resistance is improved.
xe2x80x9cHitachi power MOSFET databookxe2x80x9d issued by Semiconductor Division of Hitachi, Ltd., p47-48 describes that a diode (parasitic diode) is equivalently provided between the source and the drain of a power MOSFET and the parasitic diode has characteristics which are not inferior to those of a normal diode. It also describes that the parasitic diode can be used for a bridge circuit, an output stage of a PWM amplifier, and the like, so that an external commutation diode can be omitted. Therefore, the number of parts can be reduced.
Since the HBT has excellent characteristics such as high processing speed and low power consumption, it is being used as a semiconductor amplifying device of an RF power amplifier module or the like. FIG. 20 is a diagram showing the basic structure of a power amplifying circuit of the HBT.
As shown in FIG. 20, a heterojunction bipolar transistor (HBT) 1 employs a multi-finger structure in which a plurality of small HBT fingers 5 each having an emitter finger 2, a base finger 3, and a collector finger 4 are arranged in parallel. The fingers 2, 3, and 4 are connected in parallel with each other and connected to an emitter terminal 6, a base terminal 7, and a collector terminal 8, respectively.
In an operating mode, a power supplied from the base terminal 7 is distributed to the HBT fingers 5 and amplified. An amplified power is output to the collector fingers 4 and is further added, and a super power is output to the collector terminal 8.
In the power amplification circuit, to effectively supply the power to the load side, a load impedance 10 as a signal source is conjugate matched with an optimum impedance of the HBT via a matching circuit 11, thereby realizing characteristics of high gain and high efficiency.
Conventionally, destruction resistance of an output power amplifying device (semiconductor amplifying device) in a normal operation mode of the RF power amplifier is assured. Consequently, the output power amplifying device is not destroyed in the normal operation mode. Except for a specific example that the parasitic diode between the source and drain of an Si-MOSFET has the possibility that it operates as an equivalent protective device, a protective device is not intentionally provided for the output power amplifying device.
In the normal operation mode of a power amplifier in a mobile communication terminal such as a portable telephone, the output power amplifying device is not destroyed. It was, however, found that in the case such that the user touches the antenna of a mobile communication terminal, or a source voltage is applied in a state where an output terminal of a power amplifier is not properly terminated due to an erroneous work of an operator at the time of assembling a mobile communication terminal, the output power amplifying device of the power amplifier in the mobile communication terminal is destroyed.
FIG. 21 is a diagram schematically showing the relation between a static characteristic 15 of the power HBT and a matched load line 16. Under the matched condition, a current and a voltage on the load line are output to the load side. Under the matched condition, only a voltage lower than the breakdown voltage (BVceo) is applied to the collector terminal 8 of the HBT, so that a problem does not occur.
It was, however, found that in a practical state, when the HBT power amplifier is used for a transmitting unit of a portable telephone, the case that the matching condition particularly on the load side fluctuates from the optimal state often occurs. Specifically, as shown in FIG. 21, a load line 17, 18,or 19 that the load impedance is in an unmatched state is obtained, a voltage having an amplitude higher than that of a source voltage is applied to the collector terminal 8 in the HBT. When the voltage exceeds a device breakdown voltage, a device breakdown occurs, and it becomes a problem in practical use.
Also in an assembling work of manufacturing an RF power amplifier module by mounting an HBT on a module substrate, there is a case such that a device breakdown similarly occurs when the operator inadvertently touches a terminal or a line in the HBT. It can deteriorate the manufacturing yield of the RF power amplifier module and a wireless communication apparatus.
In order to prevent the device breakdown due to fluctuations in load, a method of setting the breakdown voltage of the HBT to a higher value can be generally considered but has a problem such that the method is not a sufficient countermeasure due to limitations of characteristics and structure.
On the other hand, in the conventional structure proposed to improve the destruction resistance of the HBT, it is difficult to perform a low voltage operation (of 2.7 to 4.2V) as the characteristic of GaAs. Since two HBTs are formed for each finger, there is a problem such that the device size (chip size) enlarges.
An object of the invention is to provide a high frequency power amplifier module and a wireless communication apparatus having a high destruction resistance to a load fluctuation.
Another object of the invention is to provide a technique capable of preventing destruction of a transistor such as a heterojunction bipolar transistor caused by fluctuations in potential due to a contact of the operator or the like at the time of manufacture of the high frequency power amplifier module and a wireless communication apparatus.
Further another object of the invention is to provide a high frequency power amplifier module and a wireless communication apparatus which operate excellently even in a state where a source voltage is lower than 5V.
Further another object of the invention is to provide a technique of realizing a smaller high frequency power amplifier module and a smaller wireless communication apparatus.
The above and other objects and novel features of the invention will become apparent from the description of the specification and the appended drawings.
Representative ones of inventions disclosed in the application will be briefly described as follows.
(1) A high frequency power amplifier module has:
an input terminal;
an output terminal;
a first voltage terminal;
a second voltage terminal;
a bias supply terminal;
a first semiconductor amplifying device having a control terminal connected to the input terminal and the bias supply terminal, a first terminal connected to the first voltage terminal, and a second terminal connected to the second voltage terminal, for supplying a signal according to a signal supplied to the input terminal from the first terminal to the output terminal; and
a first protection circuit which is a device different from a parasitic device existing in the first semiconductor amplifying device, connected to the first terminal and displays a rectifying characteristic in the forward direction in accordance with a voltage at the first terminal.
Each of the protection circuits is constructed by arranging a plurality of diodes in series.
A bias voltage of the first protection circuit is lower than a breakdown voltage between the first and second terminals with the control terminal open and is higher than a first source voltage applied to the first voltage terminal.
The protection circuit is constructed by a part of a plurality of semiconductor layers provided on a semiconductor substrate to form the semiconductor amplifying device.
The semiconductor amplifying device is formed by using any of a heterojunction bipolar transistor made of a compound semiconductor, a high electron mobility transistor made of a compound semiconductor, a field effect transistor made of a silicon semiconductor, an MESFET made of a compound semiconductor, and the like.
The heterojunction bipolar transistor has a multi-finger structure.
The heterojunction bipolar transistor is of an npn type, and the number (n) of diodes in each of the first and third protection circuits satisfies the following numerical expression:             V      cc              V      f        ≦  n  ≦            BV      ceo              V      f      
where Vcc denotes a first source voltage, Vf indicates a forward ON-state voltage of a single pn junction diode, and BVceo expresses a collector-emitter breakdown voltage with a base open.
Such a high frequency power amplifier module is assembled in a radio communication apparatus. That is, the high frequency power amplifier module is connected to the antenna of a wireless communication apparatus.
(2) The configuration of the means (1) is further provided with a second protection circuit which is a device different from a parasitic device existing in the first semiconductor amplifying device, connected to the first terminal, and displays a rectifying characteristic in the reverse direction when the first protection circuit displays the rectifying characteristic in the forward direction.
(3) The configuration of the means (1) or (2) is further provided with a third protection circuit which is a device different from a parasitic device existing in the semiconductor amplifying device, connected to the control terminal, and displays the rectifying characteristic in the forward direction in accordance with a voltage in the control terminal.
A bias voltage of the third protection circuit is lower than a breakdown voltage between first and second terminals with the control terminal open and is higher than a first source voltage applied to the first voltage terminal.
The semiconductor amplifying device is formed by using any of a heterojunction bipolar transistor made of a compound semiconductor, a high electron mobility transistor made of a compound semiconductor, a field effect transistor made of a silicon semiconductor, an MESFET made of a compound semiconductor, and the like.
The heterojunction bipolar transistor has a multi-finger structure.
The heterojunction bipolar transistor is of an npn type, and the number (n) of diodes in the third protection circuit satisfies the following numerical expression:             V      cc              V      f        ≦  n  ≦            BV      ceo              V      f      
where Vcc denotes a first source voltage, Vf indicates a forward ON-state voltage of a single pn junction diode, and BVceo expresses a collector-emitter breakdown voltage with a base open.
(4) The configuration of the means (3) is further provided with a fourth protection circuit which is a device different from a parasitic device existing in the semiconductor amplifying device, connected to the control terminal, and displays a rectifying characteristic in the reverse direction when the third protection circuit displays the rectifying characteristic.
(5) In the configuration of any one of the means (1) to (4), one or more second semiconductor amplifying devices are cascaded between the input terminal and the first semiconductor amplifying device,
the second semiconductor amplifying device has a control terminal connected to the input terminal and the bias supply terminal, outputs a signal according to a signal from the input terminal, and has a first terminal connected to the first voltage terminal, and a second terminal connected to the second voltage terminal, and
a protection circuit is provided for the first terminal and/or the control terminal of the second semiconductor amplifying device.
(6) A high frequency power amplifier module has:
an input terminal;
an output terminal;
a first transistor having a control terminal for receiving a signal from the input terminal and a first terminal for supplying a signal according to the signal supplied to the control terminal to the output terminal; and
a first protection circuit connected to the first terminal of the first transistor. The first protection circuit has a plurality of pn junction semiconductor devices connected in series.
The high frequency power amplifier module further includes a second protection circuit connected to the first terminal, the second protection circuit has a plurality of pn junction semiconductor devices connected in series, and a rectifying characteristic of the plurality of pn junction semiconductor devices connected in series is opposite to that of the plurality of pn junction semiconductor devices connected in series in the first protection circuit.
The high frequency power amplifier module further includes:
a first voltage terminal;
a second voltage terminal; and
a bias circuit connected between the first voltage terminal and the first terminal, and
the first protection circuit is connected between the first terminal and the second voltage terminal.
The second protection circuit is connected between the first terminal and the second voltage terminal.
The first and second protection circuits clamp a voltage at the first terminal by the plurality of pn junction semiconductor devices connected in series.
According to the means (1), (a) since the protection circuit in which a plurality of pn junction diodes are connected in series is connected between the collector and the emitter of each semiconductor amplifying device (for example, HBT). The p-side is connected to the collector side, and the n-side is connected to the emitter side. Consequently, when an overvoltage is applied across the collector and emitter by a fluctuation in load (load impedance) on the antenna side, the collector terminal is clamped by the ON-state voltage of the protection circuit. Thus, the HBT (semiconductor amplifying device) can be prevented from being destroyed.
(b) In the wireless communication apparatus in which such a high frequency power amplifier module is assembled, even the user touches the antenna and a fluctuation occurs in the load impedance, by the clamping effect of the protection circuit between the collector and emitter, the HBT (semiconductor amplifying device) can be prevented from being destroyed. Therefore, the user can continue conversation in an excellent state, and the reliability of communication is stabilized.
According to the means (2), in addition to the effect of the means (1), since the second protection circuit displaying the rectifying characteristic in the reverse direction when the first protection circuit displays the rectifying characteristic in the forward direction is provided, even if a load fluctuation in the reserve direction occurs, the HBT can be prevented from being destroyed by the clamping effect of the second protection circuit.
According to the means (3), in addition to the effects of the means (1) and (2), since the control terminal is provided with the third protection circuit having the rectifying characteristic in the forward direction in accordance with the voltage at the control terminal, the HBT is not destroyed by an overvoltage incidentally applied at the time of manufacturing the high frequency power amplifier module or the wireless communication apparatus.
According to the means (4), in addition to the effects of the means (3), the control terminal is provided with the fourth protection circuit displaying the rectifying characteristic in the reverse direction when the third protection circuit displays the rectifying characteristic, so that the HBT is not destroyed by an overvoltage incidentally applied at the time of manufacturing the high frequency power amplifier module or the wireless communication apparatus.
According to the means (5), also in the configuration that one or more second semiconductor amplifying devices are cascaded between the input terminal and the first semiconductor amplifying device, the first terminal and/or control terminal in the second semiconductor amplifying device is/are provided with the protection circuit. Consequently, destruction of the HBT due to a load fluctuation in the high frequency power amplifier module and the wireless communication apparatus can be prevented by the clamping effect of the protection circuit, and destruction of the HBT caused by an overvoltage incidentally generated in the manufacture of the high frequency power amplifier module and the wireless communication apparatus can be also prevented. As a result, the manufacturing yield of the high frequency power amplifier module and the wireless communication apparatus can be improved, and stable communication of the wireless communication apparatus can be achieved.
Also in the high frequency power amplifier module according to the means (6), by the clamping effect of the first and second protection circuits connected to the first terminal of the first transistor, destruction of the HBT caused by a load fluctuation and destruction of the HBT due to an overvoltage incidentally applied at the time of manufacturing the high frequency power module can be prevented.